The present invention relates to measurement probes for use with co-ordinate positioning apparatus and in particular to touch trigger measurement probes mountable in the spindle of a machine tool.
Touch trigger measurement probes for mounting in the spindle of machine tools are known. A typical measurement probe of this type comprises a workpiece-contacting stylus that can be deflected relative to the body or housing of the probe. One or more sensors are provided to measure deflection of the probe relative to the probe body and a so-called trigger signal is issued whenever a certain amount of stylus deflection has occurred to indicate that the stylus has made contact with a workpiece. This trigger signal is fed to the machine tool controller which takes a reading of the position of the machine tool spindle at the time the trigger signal is issued thereby allowing the co-ordinates of points on the surface of the workpiece to be measured.
Examples of strain gauge based touch trigger probes are described in WO2006/120403 and WO2006/100508. The probe comprises a workpiece-contacting stylus that is attached to the probe body via a sensor mechanism that comprises three strain gauges. The signals from the three strain gauges are passed to a processor which combines and analyses those signals and produces a trigger signal whenever the deflection of the workpiece-contacting stylus exceeds a predetermined deflection threshold or limit.